Silicon-based anode material for secondary battery and preparation method thereof, secondary battery

ABSTRACT

A silicon-based anode material for secondary batteries, a preparation method thereof and a secondary battery are provided. The silicon-based anode material includes: an inner core including an Si particle and silicon oxide SiO x1 , where 0&lt;x1 &lt;2, a first shell layer including a compound of the general formula M y SiO z  (0&lt;y≤4, 0&lt;z≤5, and z≥x1) and a C particle, wherein the first shell layer covers the inner core, and the contents of M and C in the first shell layer gradually increase from a side thereof close to the inner core to another side thereof far away from the inner core; and a second shell layer including a carbon film layer or a composite film layer formed by a carbon film layer and a conductive additive, the second shell layer covers the first shell layer. The first charge-discharge cycle capability of the silicon-based anode material is improved, and the manufacturing cost is reduced.

This application is a national stage application of PCT application No.PCT/CN2019/129890, filed on Dec. 30, 2019, and the contents of which isincorporated herein by reference in its entirety.

TECHNICAL FIELD

The present application relates to the field secondary batterymaterials, in particular to silicon-based anode materials for secondarybatteries, preparation methods thereof, and secondary batteries.

BACKGROUND

Conventional lithium ion batteries mainly use graphite as their anodematerial. However the theoretical capacity of graphite is only 372mAh/g, which cannot meet the high energy demand for lithium ionbatteries in the current industry. There is abundant elemental siliconin nature, and silicon is safe and environmentally friendly. Hence,silicon has attracted high attention from researchers. Moreover, intheory, silicon has a higher capacity, its capacity can reach 4200mAh/g, its discharge potential is relatively low, its price is low, andit is environmentally friendly. Thus, it can be an excellent anodematerial for lithium ion batteries. However, due to the serious volumeeffect of silicon-based materials, the cycle performance ofsilicon-based materials is very poor, which cannot meet the requirementsof commercial applications.

SiOx (0<x<2) materials have both high capacity and better cycleperformance than elemental silicon, which thus has received extensiveattention and research. However, the first charge-discharge efficiencyof SiOx (0<x<2) materials still has a large gap as compared to graphite,which makes it can hardly meet commercial needs. In the firstcharge-discharge cycle of graphite, 5% to 20% lithium is used to form apassivation film (solid electrolyte interphase film, or SEI film), andSi and SiOx (0<x<2) may consume 20-50% of lithium. Therefore, thelithium supplementation of SiOx (0<x<2) anode materials is of greatsignificance to its commercial application.

In the existing technology, a lithium layer is usually directly coatedon the surface of the electrode pole piece, or a lithium plating processis employed on the surface of the electrode pole piece to performlithium supplementation. However, on the one hand, the lithiumsupplementation process may cause excessive Si grain growth and thusreduce the cycle life of the electrode; on the other hand, the lithiumsupplementation process has poor safety performance and thus isdifficult to achieve the scale of mass production. Moreover, due to thegeneration of irreversible substances during the lithium intercalationof silicon oxide materials, the first cycle Coulombic efficiency is low,which makes it difficult for its commercial application.

SUMMARY

The present application provides a silicon-based anode material for asecondary battery and a preparation method thereof to improve the firstcharge-discharge cycle capability of the silicon-based anode materialfor a secondary battery and reduce the production cost of thesilicon-based anode material for a secondary battery.

One aspect of the present application provides a silicon-based anodematerial fix secondary batteries, comprising: an inner core, wherein theinner core including an Si particle and silicon oxide SiOx₁, where0<x₁<2; a first shell layer, wherein the first shell layer including acompound of the general formula M_(y)SiO_(z)(0<y≤4, 0<z≤5, and z≥x₁) anda C particle, the first shell layer covers the inner core, and thecontents of M and C in the first shell layer gradually increase from oneside thereof close to the inner core to another side thereof far awayfrom the inner core; and a second shell layer, wherein the second shelllayer includes a carbon film layer or a composite film layer formed of acarbon film layer and a conductive additive, and the second shell layercovers the first shell layer.

In some embodiments of the present application, M in the first shelllayer is any one or more of Li, Na, Mg, Al, Fe and Ca.

In some embodiments of the present application, the mass percentagecontent of M in the silicon-based anode material is 1-15%, wherein themass percentage of M is 1-40% of the first shell layer.

In some embodiments of the present application, the mass percentagecontent of M and C in the first shell layer increases in a gradientmanner from the side thereof close to the inner core to the side thereoffar away from the inner core.

In some embodiments of the present application, the mass percentagecontent of M on the side thereof close to the inner core is 0-5% of thefirst shell layer, and the mass percentage content of M on the sidethereof far away from the inner core is 30-48% of the first shell layer.

In some embodiments of the present application, the C particle includesany one or more of hard carbon, soft carbon, and amorphous carbon.

In some embodiments of the present application, the carbon film layerincludes any one or more of hard carbon, soft carbon, and amorphouscarbon, and the conductive addictive includes carbon nanotube, graphene,conductive carbon black, Ketjen black, vapor-grown carbon fiber,acetylene black, and conductive graphite.

In some embodiments of the present application, in the silicon-basedanode material, the mass percentage content of the C particle is 0.1-2%,the mass percentage content of the carbon film layer or the compositefilm layer formed by the carbon film layer and the conductive additiveis 0.1-15%, and the mass percentage content of the conductive additiveis 0-5%.

In some embodiments of the present application, a median diameter of theinner core is 1-10 μm, a thickness of the first shell layer is 0.01-2μm, and a thickness of the second shell layer is 0.01-1 μm.

In some embodiments of the present application, the Si particles in theinner core are uniformly dispersed in the SiOx₁.

In some embodiments of the present application, based on the mass of thesilicon-based anode material being 100%, a sum of the mass percentagecontents of the Si particle, the silicon oxide SiOx₁and the MySiO_(z)is83-99%.

In another aspect of the present application, a method for preparing asilicon-based anode material for secondary batteries is provided, andthe method comprises: preparing a first mixture, wherein the firstmixture includes a silicon oxide raw material SiO_(x) (0<x<2), a metalsource substance, and a carbon source substance; calcining the firstmixture under a non-oxygen condition to obtain a first product, whereinthe first product includes: an inner core, wherein the inner coreincludes an Si particle and silicon oxide SiOx₁, where 0<x₁<2, x₁>x; anda first shell layer, wherein the first shell layer covers the innercore, the first shell layer includes a compound of the general formulaM_(y)SiO_(z) (0<y≤4, 0<z≤5, and z≥x₁) and a C particle, the contents ofM and C in the first shell layer gradually increase from one sidethereof close to the inner core to another side thereof far away fromthe inner core; and passing the first product through a carbon sourcesubstance, or a carbon source substance and a conductive additive toperform a coating reaction, and then performing a carbonizationtreatment in a non-oxidizing atmosphere, such that a surface of thefirst shell layer is coated with a second shell layer, wherein thesecond shell layer includes a carbon film layer or a composite filmlayer formed by a carbon film layer and a conductive additive.

In some embodiments of the present application, the non-oxidizingatmosphere includes at least one of nitrogen, argon, hydrogen, orhelium.

In some embodiments of the present application, a mass ratio of thesilicon oxide raw material SiO_(x) to a metal source substance rangesfrom 100:1 to 100:50, and a mass ratio of the silicon oxide raw materialSiO_(x) to the carbon source substance ranges from 100:1 to 100:10.

In some embodiments of the present application, a temperature of thenon-oxygen condition for calcining is 300-1000° C.; and a temperature ofthe carbonization treatment is 500-1200° C.

In some embodiments of the present application, the metal sourcesubstance includes any one or more of a metal carbonate, a metal nitrateand a metal hydroxide, and the metal includes Li, Na, Mg, Al, Fe and Ca.

In some embodiments of the present application, the metal sourcesubstance includes one or more of lithium citrate, lithium carbonate,lithium hydroxide and lithium nitrate.

In some embodiments of the present application, the carbon sourcesubstance includes any one or more of citric acid, glucose, resin, coalpitch, petroleum pitch, polyvinyl alcohol, epoxy resin,polyacrylonitrile, polymethyl methacrylate, sucrose, polyacrylic acidand polyvinyl pyrrolidone.

In some embodiments of the present application, the first mixture is amixture of lithium citrate or lithium carbonate, citric acid and thesilicon oxide raw material SiO_(x) (0<x<2).

In some embodiments of the present application, the silicon oxide rawmaterial SiO_(x) is a powder with a median particle size of 1-10 μm.

In some embodiments of the present application, the percentages of themetal source substance, the carbon source substance and the siliconoxide raw material SiO_(x) are 0.1-30% and 0.1-9%, respectively.

The present application further provides a secondary battery having ananode including any of the anode materials as described in theembodiments of the present application.

The silicon-based anode material for secondary batteries described inthe embodiments of the present application improves the first cycleCoulombic efficiency of the silicon anode after the first shell layer(including M_(y)SiO_(z) and the C particle) is formed on the surface ofthe inner core (including SiO_(x1) and the Si particle). In addition,the second shell layer is coated on the surface of the first shelllayer, where the second shell layer can be, for example, a dense carbonfilm layer, or a carbon film layer and a conductive additive, whichimproves the cycle performance of the silicon-based anode material.Moreover, the conductive additive can enhance the electron migrationrate of the silicon-based anode material and improve the rapid chargingability. The structure of the silicon-based anode material is stable andsuitable for mass production.

The preparation method of the silicon-based anode material of secondarybatteries in the embodiments of the present application uses metalsource substance and carbon source substance to react with SiO_(x) togenerate a first product, certain silicates (M_(y)SiO_(z)) are alsogenerated during the reaction, thereby improving the first cycleCoulombic efficiency of silicon-based anode material. In addition, acarbon film layer or a composite film layer formed by a carbon filmlayer and a conductive additive is further coated on the outer layer ofthe first product, thereby improving the cycle performance of theprepared silicon-based anode material. Moreover, the preparation methodof the secondary battery described in the present application is simplein process, low in equipment requirements, and low in cost; and theobtained silicon-based anode material has a stable structure and can bemass-produced.

The secondary battery made of the silicon-based anode material forsecondary batteries provided by the embodiments of the presentapplication exhibits high delithiation capacity, high first cycleCoulombic efficiency and good cycle performance; its charging capacityis above 1400 mAh/g, the discharge capacity is above 1627 mAh/g, and thefirst cycle Coulombic efficiency is above 86%.

Some other features of the present application will be described in thefollowing description. Through the description, the contents in thefollowing drawings and embodiments will become obvious to a person ofordinary skill in the art. The inventive points of the presentapplication will be fully described by practicing or using the methods,means or combinations thereof set forth in the detailed examplesdiscussed below.

BRIEF DESCRIPTION OF THE DRAWINGS

The following figure illustrates in detail the exemplary embodimentsdisclosed in the present application. The same reference numeralsindicate similar structures shown in different figures. A person ofordinary skill in the art will understand that these embodiments aremerely exemplary embodiments rather than limiting embodiments. Theaccompanying drawings are only for the purpose of illustration anddescription, and are not intended to limit the scope of the presentapplication. Other embodiments may also accomplish the objects of thepresent application. Moreover, it should be understood that the drawingsare not drawn to scale.

FIG. 1 is a schematic structural diagram of a silicon-based anodematerial for secondary batteries according to some embodiments of thepresent application.

FIG. 2 is an SEM image of a silicon-based anode material according tosome embodiments of the present application.

FIG. 3 is a charge-discharge curve when the silicon-based anode materialdescribed in the embodiments of the present application is used.

DETAILED DESCRIPTION

The following description provides specific application scenarios andrequirements of the present application in order to enable a personskilled in the art to make and use the present application. Variousmodifications to the disclosed embodiments will be apparent to a personskilled in the art. The general principles defined herein may be appliedto other embodiments and applications without departing from the spiritand scope of the present application. Therefore, present application isnot limited to the embodiments described herein, but the broadest scopeconsistent with the claims.

The technical solution of the present application will be described indetail below with reference to the embodiments and accompanyingdrawings.

An aspect of the present application provides a silicon-based anodematerial secondary batteries, referring to FIG. 1, including:

an inner core 10, where the inner core 10 includes an Si particle andsilicon oxide SiO_(x1), where 0<x1<2;

a first shell layer 11, where the first shell layer 11 includes acompound of the general formula M_(y)SiO_(z) (0<y≤4, 0<z≤5, and z≥x₁)and a C particle, the first shell layer 11 covers the inner core 10, thecontents of M and C in the first shell layer 11 gradually increase fromthe side close to the inner core 10 to the side far away from the innercore 10, and the contents of Si and O gradually decrease from the sideclose to the inner core 10 to the side far away from the inner core 10;

a second shell layer 12, where the second shell layer 12 includes acarbon film layer or a composite film layer formed by a carbon filmlayer and a conductive additive, and the second shell layer 12 coversthe first shell layer 11.

In some embodiments of the present application, the silicon oxideSiO_(x1) (0<x1 <2) contained in the inner core is a powder, and the Siparticle exists in the state of a silicon particle of elemental silicon.The Si particle and the silicon oxide SiO_(x1) exist in the form of amixture to constitute the inner core of the silicon-based anodematerial. Moreover, the Si particles are uniformly dispersed in theSiO_(x1), and the “uniformly” herein does not refer to being completelyuniformly dispersed, but being substantially uniformly dispersed.

The first shell layer 11 covers the inner core 10, and it may partiallycover the inner core 10 or completely cover the inner core 10. By way ofmost types of the manufacturing processes for silicon-based anodematerials, the inner shell 10 can be completely covered by the firstshell layer 11. FIG. 1 schematically shows the case of completelycoating. However, the first shell layer 11 is not necessarily a perfectcircular coating structure, as long as the coating thickness of thefirst shell layer 11 is generally close to each other at differentlocations.

In some embodiments of the present application, the first shell layer 11includes a compound of the general formula M_(y)SiO_(z) (0<y≤4, 0<z≤5,and z≥x₁) and a C particle, where M may be any one or more of Li, Na,Mg, Al, Fe and Ca, for example, M_(y)SiO_(z) is Li₂SiO₃, Li₂Si₂O₅,Li₄SiO₄, MgSiO₃, CaSiO₃, FeSiO₃ or the like.

In some embodiments of the present application, the contents of M and Cin the first shell layer 11 gradually increase from a side close to theinner core 10 to a side far away from the inner core 10, and thecontents of Si and O gradually decrease from the side close to the innercore to the far away from the inner core 10. The gradual increase hereinmay be an uneven increase or an even monotonous increase, and thegradual decrease herein may be an uneven decrease or an even monotonousdecrease. For example, the content may increase from 3% to 45% in alinear manner, or it may increase from 4% to 30% in a linear manner.

In some other embodiments of the present application, the masspercentage content of the M element in the first shell layer increasesfrom the side close to the inner core to the side away from the innercore in a gradient manner. For example, the mass percentage content of Min the first shell layer is first maintained at a certain level of 3.5%for a certain thickness, then increased to the level of 11.5% for acertain thickness, increased to 19.5% for a certain thickness, increasedto 27.5% for a certain thickness, and next increased to 35.5% for acertain thickness.

In some embodiments of the present application, overall the masspercentage content of M on the side close to the inner core accounts for0-5% of the first shell layer, and the mass percentage content of M onthe side far away from the inner core accounts for 30-48% of the firstshell layer. Based on the mass of the first shell layer being 100%, theoverall average content of M in terms of mass percentage of the firstshell layer is 1-40%.

In some embodiments of the present application, the C particle may beany one or more of hard carbon, soft carbon, or amorphous carbon, andthe C particle exists in the form of elemental carbon. The role of the Cparticle is to limit the size of the silicon particle while improvingthe electrical conductivity of the first shell layer. The C particles inthe first shell layer are uniformly dispersed in M_(y)SiO_(z).

In the silicon-based anode material (based on the mass of thesilicon-based anode material being 100%), the mass percentage content ofthe M element is 1% to 15%, for example, 2%, 4%, 5%, 8%, 10%, 12%, 14%,etc. The mass percentage content of the C particle is 0.1% ˜2%, such as0.2%, 0.4%, 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, etc.

In some embodiments of the present application, based on the mass of thesilicon-based anode material being 100%, the sum of the mass percentagecontents (Wt) of the Si particles, silicon oxide SiO_(x1) andM_(y)SiO_(z) is 83% ˜99%, for example, 87%, 90%, 92%, 95%, 97%, etc.Among them, the mass percentage content of silicon oxide SiO_(x1) (Wt₂)ranges from 55 to 75%, the mass percentage content of M_(y)SiO_(z)compound (Wt₃) ranges from 1 to 20%, and the mass percentage content ofSi particles Wt₁ ranges from (Wt₁=Wt−Wt₂−Wt₃).

In some embodiments of the present application, the second shell layer12 covers the first shell layer 11. The second shell layer 12 mayinclude only a carbon film layer, and may also include a composite filmlayer formed of a carbon film layer and a conductive additive, whereinthe conductive additive is uniformly dispersed in the carbon film layerto form the second shell layer. The second shell layer completely coversthe first shell layer to prevent the silicon-containing materials(including Si particle, silicon oxide SiO_(x1) and M_(y)SiO_(z)) in thefirst shell layer and inner core from directly contacting theelectrolyte, slowing down the surface powdering of the silicon-basedanode material and prolong the cycle life. The conductive additive isused to increase the conductivity of the silicon-based anode material.

In some embodiments of the present application, in the silicon-basedanode material, the mass percentage content of the carbon film layer orthe composite film layer formed by the carbon film layer and theconductive additive is 0.1-15%, and the mass percentage content of theconductive additive is 0-5%.

The carbon film layer material includes any one or more of hard carbon,soft carbon, or amorphous carbon, and the conductive additive includesany one or more of carbon nanotubes, graphene, conductive carbon black,Ketjen black, vapor grown carbon fiber, acetylene black, and conductivegraphite.

In some embodiments of the present application, the median diameter ofthe inner core is 1-10 μm, and the thickness of the first shell layer is0.01-2 μm. The thickness of the second shell layer is 0.01-2 μm.

The silicon-based anode material for secondary batteries described inthe embodiments of the present application improves the first coulombicefficiency of the silicon anode after forming the first shell layer(M_(y)SiO_(z) and C particle) on the inner core (SiO_(x1) and Siparticle) surface; The layer is coated with a second shell layer, thesecond shell layer is, for example, a dense carbon film layer or acomposite film layer of carbon film layer and conductive additive, whichimproves the cycle performance of the silicon-based anode material,moreover, the conductive additive can enhance the electron migrationrate of the silicon-based anode material and improve the rapid chargingability; the structure of the silicon-based anode material is stable andmass production can be achieved.

Further, the contents of M and C in the first shell layer of thesilicon-based anode material gradually increases from the side close tothe inner core to the side far away from the inner core. This change inmaterial concentration is beneficial to improve the structural stabilityof the silicon-based anode material and reduce the expansion stress ofthe second shell layer. Furthermore, when the contents of the M and Cincrease gradually from the side close to the inner core to the side faraway from the inner core, the formed concentration gradient can improvethe stability of the silicon-based anode material structure and reducethe expansion stress of the second shell layer.

Another aspect of the present application provides a method forpreparing a silicon-based anode material for secondary batteries,including:

Step S1, a first mixture is prepared, where the first mixture includes asilicon oxide raw material SiO_(x), a metal source substance, and acarbon source substance (where 0<x <2);

In the above step, the silicon oxide raw material SiO_(x) is a powderwith a median diameter D50 of 1 to 10 μm. The method for forming thesilicon oxide raw material SiO_(x) powder may be, for example, to obtainthe SiO_(x) powder by coarsely crushing and pulverizing a bulk materialof SiO_(x) . The coarse crushing step includes using a jaw crusher, aroller crusher, a conical crusher, a hammer crusher or an impact crusherto coarsely crush the bulk material of SiO_(x). The pulverizing stepincludes using any one of an air jet crusher, a mechanical crusher, aball mill, or a vibratory mill to further crush the coarsely crushedSiO_(x) to obtain a powder with a median particle size of 1-10 μm.

The method fix preparing the first mixture my employs, for example, anyone of a high-speed dispersing machine, a high-speed stirring mill, aball mill, a conical mixer, a spiral mixer, a stirring mixer, or a VCmixer to mix a powder form silicon oxide raw material SiO_(x) uniformlywith the metal source substance and the carbon source substance.

In some embodiments of the present application, the metal sourcesubstance may include any one or more of a metal carbonate, a metalnitrate, and a metal hydroxide, where the metal may be Li, Na, Mg, Al,Fe or Ca. For example, the metal source substance may include one ormore of lithium citrate, lithium carbonate, lithium hydroxide or lithiumnitrate; the carbon source substance may include any one or more ofcitric acid, glucose, resin, coal pitch, petroleum pitch, polyvinylalcohol, epoxy resin, polyacrylonitrile, polymethyl methacrylate,sucrose, polyacrylic acid and polyvinyl pyrrolidone.

In some embodiments of the present application, the metal sourcesubstance may be lithium citrate or lithium carbonate, the carbon sourcesubstance may be citric acid, and the first mixture may be a mixture oflithium citrate or lithium carbonate, citric acid, and SiO_(x) (0<x <2).

In some embodiments of the present application, the mass ratio of thesilicon oxide raw material SiO_(x) to the metal source substance rangesfrom 100:1 to 100:50, and the mass ratio of the silicon oxide rawmaterial SiO_(x) to the carbon source substance ranges from 100:1 to100:10. That is, as the mass of the silicon oxide raw material SiO_(x)being 100 g, the mass of the metal source substance is 1-50 g, and themass of the carbon source substance is 1-10 g.

Step S2, calcining the first mixture under non-oxygen conditions toobtain a first product, where the first product includes:

an inner core, wherein the inner core includes an Si particle andsilicon oxide SiOx₁, where 0<x₁<2, x₁>x; and

a first shell layer, wherein the first shell layer covers the innercore, the first shell layer includes a compound of the general formulaM_(y)SiO_(z) (0<y≤4, 0<z≤5, and z≥x₁>x) and a C particle, the contentsof M and C in the first shell layer gradually increase from one sidethereof close to the inner core to another side thereof far away fromthe inner core; and the contents of Si and O in the first shell layergradually decrease from one side thereof close to the inner core toanother side thereof far away from the inner core.

In some embodiments of the present application, the non-oxidizingatmosphere refers to that the reaction gas includes at least one ofnitrogen, argon, hydrogen, or helium. In some embodiments of the presentapplication, the calcining temperature under the non-oxygen conditionsmay be 300° C. -1000° C., and the calcining time may be 1-24 hours. Forexample, the calcining temperature is 400° C., 500° C., 600° C., 700°C., 800° C., 900° C., etc. The calcining time is 2 hours, 4 hours,hours, 6 hours, 8 hours, 11 hours, 13 hours, 16 Hours, 18 hours, 21hours, etc.

The equipment for performing the calcination process may be, forexample, any one of a rotary furnace, a roller track kiln, a push platekiln, an atmosphere box furnace, or a tube furnace. By means ofadjusting the content of the first mixture to be reacted, theconcentrations of the metal source substance and carbon sourcesubstance, as well as the reaction time and temperature of thecalcination process, the contents of M and C in the first shell layergradually increase from the side close to the inner core to the side faraway from the inner core, while the contents of Si and O graduallydecrease from the side close to the inner core to the side far away fromthe inner core. That is to say, in the embodiments of the presentapplication, by means of controlling the time, temperature and reactionconcentration ratio of the metal source substance M and the inner coresubstance (Si particle and silicon, oxide SiO_(x1)), the generation ofM_(y)SiO_(z) and the M and C contents in the first shell layer from theside close to the inner core to the side far away from the inner corecan be controlled.

Step S3, the first product is coated with carbon source substance or amixture of a carbon source substance and a conductive additive; next, acarbonization treatment is performed in a non-oxidizing atmosphere, suchthat the surface of the first shell layer is coated with a second shelllayer, where the second shell layer includes a carbon film layer or acomposite film layer formed by a carbon film layer and a conductiveadditive.

In some embodiments of the present application, the equipment that canperform the foregoing coating reaction may be any one of a mechanicalfusion machine, a VC mixer, a coating kettle, a spray dryer, a sandmill, or a high-speed disperser. The non-oxidizing atmosphere refers tothat the reaction gas includes at least one of nitrogen, argon,hydrogen, or helium.

The carbon source substance includes any one or more of citric acid,glucose, resin, coal pitch, petroleum pitch, polyvinyl alcohol, epoxyresin, polyacrylonitrile, polymethyl methacrylate, sucrose, polyacrylicacid and polyvinyl pyrrolidone. The temperature for the carbonizationtreatment is 500-1200° C., and the treatment time is 1-12 hours. Forexample, the temperature for the carbonization treatment is 600° C.,700° C., 800° C., 900° C., 1000° C., 1100° C., etc. The treatment timeis 2 hours, 4 hours, hours, 6 hours, 8 hours, 11 hours, etc.

The carbon film layer in this case includes any one or more of hardcarbon, soft carbon or amorphous carbon. The conductive additiveincludes any one or more of carbon nanotube, graphene, conductive carbonblack, Ketjen black, vapor-grown carbon fiber, acetylene black,conductive graphite, and the like.

The method for preparing the silicon-based anode material of secondarybatteries provided in the embodiments of the present application usesmetal source substance and carbon source substance to react with SiO_(x)so as to generate a first product, silicate (M_(y)SiO_(z)) is alsogenerated during the reaction, thereby improving the first cycleCoulombic efficiency of the silicon-based anode material. Moreover, bymeans of coating a carbon film layer or a composite film layer of acarbon film layer and a conductive additive on the outer surface thefirst product, the cycle performance of the prepared silicon-based anodematerial can be improved. Furthermore, the preparation method of thesecondary battery as described in the present application is simple inprocess, low in equipment requirements, and low in cost; and theobtained silicon-based anode material has a stable structure and thuscan be mass-produced.

The present application further provides a secondary battery having ananode including any of the anode materials described in the embodimentsof the present application.

EXAMPLE 1

Bulk SiO_(x) (x =0.9) is coarsely crushed using a roller crusher, andthen the coarsely crushed raw material is next pulverized by a jet millto obtain a SiO_(x) powder with a particle size D50 of 5 μm, theobtained SiO_(x) powder is thoroughly mixed with lithium carbonate andcitric acid in a high-speed stirring mill to prepare a first mixtureincluding lithium carbonate, citric acid and SiO_(x). In this case, themass of the silicon oxide raw material SiO_(x) is 1 kg, the mass of thelithium carbonate is 476.8 g, and the mass of the citric acid is 5 g.

The first mixture is calcined in a rotary furnace in an argon atmosphereat a calcining temperature of 750° C. and for a reaction time of 12 h toobtain a first product including an inner core, which includes SiO_(x1)and Si particle, and a first shell layer, which includes Li₂SiO₃ and a Cparticle.

The first product is then subjected to a coating reaction with aconductive graphite-doped pitch in a coating kettle. The coalingreaction is carried out in an argon atmosphere, the reaction temperatureis 600° C., and the reaction time is 10 hours. Finally, a silicon-basedanode material is obtained, which includes the inner core includingSiO_(x1) and the Si particle, the first shell layer including Li₂SiO₃and the C particle, and a second shell layer, which is a carbon filmlayer doped with conductive graphite.

The mass percentage content of Li in the silicon-based anode material is10%, where the mass percentage content of Li in the inner side of thefirst shell layer is 4%, and the mass percentage content of Li in theouter side of the first shell layer is 45%. The secondary battery madewith the foregoing silicon-based anode material has a reversiblecapacity of 1430 mAh/g, a first cycle Coulombic efficiency of 89%, and a500-cycles capacity retention rate of 88%.

EXAMPLE 2

Bulk SiO_(x) (x=0.9) is coarsely crushed using a roller crusher, andthen the coarsely crushed raw material is next pulverized by a jet millto obtain a SiO_(x) powder with a particle size D50 of 5 μm, theobtained SiO_(x) powder is thoroughly mixed with lithium carbonate andcitric acid in a high-speed stirring mill to prepare a first mixture,including lithium carbonate, citric acid and SiO_(x). In this case, themass of the silicon oxide raw material SiO_(x) is 1 kg, the mass of thelithium citrate is 286.1 g, and the mass of the citric acid is 5 g.

The first mixture is calcined in a rotary furnace in an argon atmosphereat a calcining temperature of 750° C. and for a reaction time of 12 h toobtain a first product including an inner core, which includes SiO_(x1)and Si particle, and a first shell layer, which includes Li₂SiO₃ and a Cparticle.

The first product is then subjected to a coating reaction with aconductive graphite-doped pitch in a coating kettle. The coatingreaction is carried out in an argon atmosphere, the reaction temperatureis 600° C., and the reaction time is 10 hours. Finally, a silicon-basedanode material is obtained, which includes the inner core includingSiO_(x1) and the Si particle, the first shell layer including Li₂SiO₃and the C particle, and a second shell layer, which is a carbon filmlayer doped with conductive graphite.

The mass percentage content of Li in the silicon-based anode material is6%, where the mass percentage content of M in the inner side of thefirst shell layer is 2.5%, and the mass percentage content of M in theouter side of the first shell layer is 36%. The secondary battery madewith the foregoing silicon-based anode material has a reversiblecapacity of 1500 mAh/g, a first cycle Coulombic efficiency of 85%, and a500-cycles capacity retention rate of 85%.

EXAMPLE 3

Bulk SiO_(x) (x=0.9) is coarsely crushed using a roller crusher, andthen the coarsely crushed raw material is next pulverized by a jet millto obtain a SiO_(x) powder with a particle size D50 of 5 μm, theobtained SiO_(x) powder is thoroughly mixed, with lithium carbonate andcitric acid in a high-speed stirring mill to prepare a first mixtureincluding lithium carbonate, citric acid and SiO_(x). In this case, themass of the silicon oxide raw material SiO_(x) is 1 kg, the mass of thelithium carbonate is 95.4 g, and the mass of the citric acid is 5 g.

The first mixture is calcined in a rotary furnace in an argon atmosphereat a calcining temperature of 750° C. and for a reaction time of 12 h toobtain a first product including an inner core, which includes SiO_(x1)and Si particle, and a first shell layer, which includes Li₂SiO₃ and a Cparticle.

The first product is then subjected to a coating reaction with aconductive graphite-doped pitch in a coating kettle. The coatingreaction is carried out in an argon atmosphere, the reaction temperatureis 600° C., and the reaction time is 10 hours. Finally, a silicon-basedanode material is obtained, which includes the inner core includingSiO_(x1) and the Si particle, the first shell layer including Li₂SiO₃and the C particle, and a second shell layer, which is a carbon filmlayer doped with conductive graphite.

The mass percentage, content of M in the silicon-based anode material is2%, where the mass percentage content of Li in the inner side of thefirst shell layer is 0.5%, and the mass percentage content of M in theouter side of the first shell layer is 21%. The secondary battery madewith the foregoing silicon-based anode material has a reversiblecapacity of 1500 mAh/g, a first cycle Coulombic efficiency of 82%, and a500-cycles capacity retention rate of 78%.

Example 4

Bulk SiO_(x) (x=0.9) is coarsely crushed using a roller crusher, andthen the coarsely crushed raw material is next pulverized by a jet millto obtain a SiO_(x) powder with a particle size D50 of 5 μm, theobtained SiO_(x) powder is thoroughly mixed with lithium carbonate andcitric acid in a high-speed stirring mill to prepare a first mixtureincluding lithium carbonate, citric acid and SiO_(x). In this case, themass of the silicon oxide raw material SiO_(x) is 1 kg, the mass of thelithium carbonate is 476.8 g, and the mass of the citric acid is 5 g.

The first mixture is calcined in a rotary furnace in an argon atmosphereat a calcining temperature of 850° C. and for a reaction time of 12 h toobtain a first product including an inner core, which includes SiO_(x1)and Si particle, and a first shell layer, which includes Li₂SiO₃,Li₂Si₂O₅ and a C particle.

The first product is then subjected to a coating reaction with aconductive graphite-doped pitch in a coating kettle. The coatingreaction is carried out in an argon atmosphere, the reaction temperatureis 600° C., and the reaction time is 10 hours. Finally, a silicon-basedanode material is obtained, which includes the inner core includingSiO_(x1) and the Si particle, the first shell layer including Li₂SiO₃,Li₂Si₂O₅ and the C particle, and a second shell layer, which is a carbonfilm layer doped with conductive graphite.

The mass percentage content of Li in the silicon-based anode material is10%, where the mass percentage content of Li in the inner side of thefirst shell layer is 4.5%, and the mass percentage content of Li in theouter side of the first shell layer is 44.5%. The secondary battery madewith the foregoing silicon-based anode material has a reversiblecapacity of 1430 mAh/g, a first cycle Coulombic efficiency of 88%, and a500-cycles capacity retention rate of 90%.

EXAMPLE 5

Bulk SiO_(x) (x=0.9) is coarsely crushed using a roller crusher, andthen the coarsely crushed raw material is next pulverized by a jet millto obtain a SiO_(x) powder with a particle size D50 of 5 μm, theobtained SiO_(x) powder is thoroughly mixed with lithium carbonate andcitric acid in a high-speed stirring mill to prepare a first mixtureincluding lithium carbonate, citric acid and SiO_(x). In this case, themass of the silicon oxide raw material SiO_(x) is 1 kg, the mass of thelithium carbonate is 476.8 g, and the, mass of the citric acid is 5 g.

The first mixture is calcined in a rotary furnace in an argon atmosphereat a calcining temperature of 950° C. and for a reaction time of 12 h toobtain a first product including an inner core, which includes SiO_(x1)and Si particle, and a first shell layer, which includes Li₂SiO₃,Li₄SiO₄ and a C particle.

The first product is then subjected to a coating reaction with aconductive graphite-doped pitch in a coating kettle. The coatingreaction is carried out in an argon atmosphere, the reaction temperatureis 600° C., and the reaction time is 10 hours. Finally, a silicon-basedanode material is obtained, which includes the inner core includingSiO_(x1) and the Si particle, the first shell layer including Li₂SiO₃,Li₄SiO₄ and the C particle, and a second shell layer, which is a carbonfilm layer doped with conductive graphite.

The mass percentage, content of Li in the silicon-based anode materialis 10%, where the mass percentage content of Li in the inner side of thefirst shell layer is 5%, and the mass percentage content of Li in theouter side of the first shell layer is 43%. The secondary battery madewith the foregoing silicon-based anode material has a reversiblecapacity of 1400 mAh/g, a first cycle Coulombic efficiency of 90%, and a500-cycles capacity retention rate of 86%.

EXAMPLE 6

Bulk SiO_(x) (x=0.9) is coarsely crushed using a roller crusher, andthen the coarsely crushed raw material is next pulverized by a jet millto obtain a SiO_(x) powder with a particle size D50 of 5 μm, theobtained SiO_(x) powder is thoroughly mixed with lithium carbonate andcitric acid in a high-speed stirring mill to prepare a first mixtureincluding lithium carbonate, citric acid and SiO_(x). In this case, themass of the silicon oxide raw material SiO_(x) is 1 kg, the mass of thelithium carbonate is 476.8 g, and the mass of the citric acid is 5 g.

The first mixture is calcined in a rotary furnace in an argon atmosphereat a calcining temperature of 750° C. and for a reaction time of 8 h toobtain a first product including an inner core, which includes SiO_(x1)and Si particle, and a first shell layer, which includes Li₂SiO₃ and a Cparticle.

The first product is then subjected to a coating reaction with aconductive graphite-doped pitch in a coating kettle. The coatingreaction is carried out in an argon atmosphere, the reaction temperatureis 600° C., and the reaction time is 10 hours. Finally, a silicon-basedanode material is obtained, which includes the inner core includingSiO_(x1) and the Si particle, the first shell layer including Li₂SiO₃and the C particle, and a second shell layer, which is a carbon filmlayer doped with conductive graphite.

The mass percentage content of Li in the silicon-based anode material is10%, where the mass percentage content of Li in the inner side of thefirst shell layer is 3%, and the mass percentage content of Li in theouter side of the first shell layer is 46%. The secondary battery madewith the foregoing silicon-based anode material has a reversiblecapacity of 1350 mAh/g, a first cycle Coulombic efficiency of 86%, and a500-cycles capacity retention rate of 85%.

EXAMPLE 7

Bulk SiO_(x) (x=0.9) is coarsely crushed using a roller crusher, andthen the coarsely crushed raw material is next pulverized by a jet millto obtain a SiO_(x) powder with a particle size D50 of 5 μm, theobtained SiO_(x) powder is thoroughly mixed with lithium carbonate andcitric acid in a high-speed stirring mill to prepare a first mixtureincluding lithium carbonate, citric acid and SiO_(x). In this case, themass of the silicon oxide raw material SiO_(x) is 1 kg, the mass of thelithium carbonate is 476.8 g, and the mass of the citric acid is 5 g.

The first mixture is calcined in a rotary furnace in an argon atmosphereat a calcining temperature of 750° C. and for a reaction time of 16 h toobtain a first product including an inner core, which includes SiO_(x1)and Si particle, and a first shell layer, which includes Li₂SiO₃ and a Cparticle.

The first product is then subjected to a coating reaction with aconductive graphite-doped pitch in a coating kettle. The coatingreaction is carried in an argon atmosphere, the reaction temperature is600° C., and the reaction time is 10 hours. Finally, a silicon-basedanode material is obtained, which includes the inner core includingSiO_(x1) and the Si particle, the first shell layer including Li₂SiO₃and the C particle, and a second shell layer, which is a carbon filmlayer doped with conductive graphite.

The mass percentage content of Li in the silicon-based anode material is10%, where the mass percentage content of Li in the inner side of thefirst shell layer is 3%, and the mass percentage content of Li in theouter side of the first shell layer is 46%. The secondary battery madewith the foregoing silicon-based anode material has a reversiblecapacity of 1350 mAh/g, a first cycle Coulombic efficiency of 86%, and a500-cycles capacity retention rate of 85%.

EXAMPLE 8

Bulk SiO_(x) (x=0.9) is coarsely crushed using a roller crusher, andthen the coarsely crushed raw material is next pulverized by a jet millto obtain a SiO_(x) powder with a particle size D50 of 5 μm, theobtained SiO_(x) powder is thoroughly mixed with sodium hydroxide andcitric acid in a high-speed stirring mill to prepare a first mixtureincluding sodium hydroxide, citric acid and SiO_(x). In this case, themass of the silicon oxide raw material SiO_(x) is 1 kg, the mass of thesodium hydroxide is 193.2 g, and the mass of the citric acid is 5 g.

The first mixture is calcined in a rotary furnace in an argon atmosphereat a calcining temperature of 750° C. and for a reaction time of 12 h toobtain a first product including an inner core, which includes SiO_(x1)and Si particle, and a first shell layer, which includes Na₂SiO₃ and a Cparticle.

The first product is then subjected to a coating reaction with aconductive graphite-doped pitch in a coating kettle. The coatingreaction is carried out in an argon atmosphere, the reaction temperatureis 600° C., and the reaction time is 10 hours. Finally, a silicon-basedanode material obtained, which includes the inner core includingSiO_(x1) and the Si particle, the first shell layer including Na₂SiO₃and the C particle, and a second shell layer, which is a carbon filmlayer doped with conductive graphite.

The mass percentage content of Na in the silicon-based anode material is10%, where the mass percentage content of Na in the inner side of thefirst shell layer is 2%, and the mass percentage content of Li in theouter side of the first shell layer is 46%. The secondary battery madewith the foregoing silicon-based anode material has a reversiblecapacity of 1200 mAh/g, a first cycle Coulombic efficiency of 78%, and a500-cycles capacity retention rate of 83%.

EXAMPLE 9

Bulk SiO_(x) (x=0.9) is coarsely crushed using a roller crusher, andthen the coarsely crushed raw material is next pulverized by a jet millto obtain a SiO_(x) powder with a particle size D50 of 5 μm, theobtained SiO_(x) powder is thoroughly mixed with magnesium carbonate andcitric acid in a high-speed stirring mill to prepare a first mixtureincluding magnesium carbonate, citric acid and SiO_(x). In this case,the mass of the silicon oxide raw material SiO_(x) is 1 kg, the mass ofthe magnesium carbonate is 466.5 g, and the mass of the citric acid is 5g.

The first mixture is calcined in a rotary furnace in an argon atmosphereat a calcining temperature of 950° C. and for a reaction time of 12 h toobtain a first product including an inner core, which includes SiO_(x1)and Si particle, and a first shell layer, which includes MgSiO₃ and a Cparticle.

The first product is then subjected to a coating reaction with aconductive graphite-doped pitch in a coating kettle. The coatingreaction is carried out in an argon atmosphere, the reaction temperatureis 600° C., and the reaction time is 10 hours. Finally, a icon-basedanode material is obtained, which includes the inner core includingSiO_(x1) and the Si particle, the first shell layer including MgSiO₃ andthe C particle, and a second shell layer, which is a carbon film layerdoped with conductive graphite.

The mass percentage content of Mg in the silicon-based anode material is12%, where the mass percentage content of Mg in the inner side of thefirst shell layer is 3%, and the mass percentage content of Mg in theouter side of the first shell layer is 46%. The secondary battery madewith the foregoing silicon-based anode material has a reversiblecapacity of 1400 mAh/g, a first cycle Coulombic efficiency of 82%, and a500-cycles capacity retention rate of 85%.

EXAMPLE 10

Bulk SiO_(x) (x=0.9) is coarsely crushed using a roller crusher, andthen the coarsely crushed raw material is next pulverized by a jet millto obtain a SiO_(x) powder with a particle size D50 of 5 μm, theobtained SiO_(x) powder is thoroughly mixed with aluminum hydroxide andcitric acid in a high-speed stirring mill to prepare a first mixtureincluding aluminum hydroxide, citric acid and SiO_(x). In this case, themass of the silicon oxide raw material SiO_(x) is 1 kg, the mass of thealuminum hydroxide is 353.1 g, and the mass of the citric acid is 5 g.

The first mixture is calcined in a rotary furnace in an argon atmosphereat a calcining temperature of 1000° C. and for a reaction time of 12 hto obtain a first product including an inner core, which includesSiO_(x1) and Si particle, and a first shell layer, which includesAlSi_(1.5)O_(4.5) and a C particle.

The first product is then subjected to a coating reaction with aconductive graphite-doped pitch in a coating kettle. The coatingreaction is carried out in an argon atmosphere, the reaction temperatureis 600° C., and the reaction time is 10 hours. Finally, a silicon-basedanode material is obtained, which includes the inner core includingSiO_(x1) and the Si particle, the first shell layer includingAlSi_(1.5)O_(4.5) and the C particle, and a second shell layer, which isa carbon film layer doped with conductive graphite.

The mass percentage content of Al in the silicon-based anode material is10%, where the mass percentage content of Al in the inner side of thefirst shell layer is 4%, and the mass percentage content of Al in theouter side of the first shell layer is 45%. The secondary battery madewith the foregoing silicon-based anode material has a reversiblecapacity of 1430 mAh/g, a first cycle Coulombic efficiency of 89%, and a500-cycles capacity retention rate of 88%.

EXAMPLE 11

Bulk SiO_(x) (x=0.9) is coarsely crushed using a roller crusher, andthen the coarsely crushed raw material is next pulverized by a jet millto obtain a SiO_(x) powder with a particle size D50 of 5 μm, theobtained SiO_(x) powder is thoroughly mixed with ferric hydroxide andcitric acid in a high-speed stirring mill to prepare a first mixtureincluding ferric hydroxide, citric acid and SiO_(x). In this case, themass of the silicon oxide raw material SiO_(x) is 1 kg, the mass of theferric hydroxide is 297.4 g, and the mass of the citric acid is 5 g.

The first mixture is calcined in a rotary furnace in an argon atmosphereat a calcining temperature of 1000° C. and for a reaction time of 12 hto obtain a first product including an inner core, which includesSiO_(x1) and Si particle, and a first shell layer, which includes FeSiO₃and a C particle.

The first product is then subjected to a coating reaction with aconductive graphite-doped pitch in a coating kettle. The coatingreaction is carried in an argon atmosphere, the reaction temperature is600° C., and the reaction time is 10 hours. Finally, a silicon-basedanode material is obtained, which includes the inner core includingSiO_(x1) and the Si particle, the first shell layer including FeSiO₃ andthe C particle, and a second shell layer, which is a carbon film layerdoped with conductive graphite.

The mass percentage content of Fe in the silicon-based anode material is14%, where the mass percentage content of Fe in the inner side of thefirst shell layer is 3%, and the mass percentage content of Fe in theouter side of the first shell layer is 46%. The secondary battery madewith the foregoing silicon-based anode material has a reversiblecapacity of 1240 mAh/g, a first cycle Coulombic efficiency of 75%, and a500-cycles capacity retention rate of 65%.

EXAMPLE 12

Bulk SiO_(x) (x=0.9) is coarsely crushed using a roller crusher, andthen the coarsely crushed raw material is next pulverized by a jet millto obtain a SiO_(x) powder with a particle size D50 of 5 μm, theobtained SiO_(x) powder is thoroughly mixed with calcium carbonate andcitric acid in a high-speed stirring mill to prepare a first mixtureincluding calcium carbonate, citric acid and SiO_(x). In this case, themass of the silicon oxide raw material SiO_(x) is 1 kg, the mass of thecalcium carbonate is 277.8 g, and the mass of the citric acid is 5 g.

The first mixture is calcined in a rotary furnace in an argon atmosphereat a calcining temperature of 1000° C. and for a reaction time of 12 hto obtain a first product including an inner core, which includesSiO_(x1) and Si particle, and a first shell layer, which includes CaSiO₃and a C particle.

The first product is then subjected to a coating reaction with aconductive graphite-doped pitch in a coating kettle. The coatingreaction carried out in an argon atmosphere, the reaction temperature is600° C., and the reaction time is 10 hours. Finally, a silicon-basedanode material is obtained, which includes the inner core includingSiO_(x1) and the Si particle, the first shell layer including CaSiO₃ andthe C particle, and a second shell layer, which is a carbon film layerdoped with conductive graphite.

The mass percentage content of Ca in the silicon-based anode material is10%, where the mass percentage content of Ca in the inner side of thefirst shell layer is 2%, and the mass percentage content of Ca in theouter side of the first shell layer is 45%. The secondary battery madewith the foregoing silicon-based anode material has a reversiblecapacity of 1140 mAh/g, a first cycle Coulombic efficiency of 65%, and a500-cycles capacity retention rate of 62%.

Comparative Example 1

Bulk SiO_(x) (x=0.9) is coarsely crushed using a roller crusher, andthen the coarsely crushed raw material is next pulverized by a jet millto obtain a SiO_(x) powder with a particle size D50 of 5 μm, theobtained SiO_(x) powder is thoroughly mixed with citric acid in ahigh-speed stirring mill to prepare a first mixture including citricacid and SiO_(x). In this case, the mass of the silicon oxide rawmaterial SiO_(x) is 1 kg and the mass of the citric acid is 5 g.

The first mixture is calcined in a rotary furnace in an argon atmosphereat a calcining temperature of 700° C. to obtain a first productincluding an inner core, which includes SiO_(x1) and Si particle, and ashell of the C particle.

The first product is then subjected to a coating reaction with aconductive graphite-doped pitch in a coating kettle. The coatingreaction is carried out in an argon atmosphere, the reaction temperatureis 750° C., and the reaction time is 12 hours. Finally, a silicon-basedanode material is obtained, which includes an inner core including SiOx1and the Si particle, and an outer shell layer of a carbon film layerdoped with conductive graphite.

The secondary battery made with the foregoing silicon-based anodematerial has a reversible capacity of 1650 mAh/g, a first cycleCoulombic efficiency of 76%, and a 500-cycles capacity retention rate of30%.

Comparative Example 2

Bulk SiO_(x) (x=0.9) is coarsely crushed using a roller crusher, an thenthe coarsely crushed raw material is next pulverized by a jet mill toobtain a SiO_(x) powder with a particle size D50 of 5 μm, the obtainedSiO_(x) powder is thoroughly mixed with citric acid in a high-speedstirring mill to prepare a first mixture including citric acid andSiO_(x). In this case, the mass of the silicon oxide raw materialSiO_(x) is 1 kg and the mass of the citric acid is 10 g.

The first mixture is calcined in a rotary furnace in an argon atmosphereat a calcining temperature of 700° C. to obtain a first productincluding an inner core, which includes SiO_(x1) and Si particle, and anouter shell of the C particle.

The first product is then subjected to a coating reaction with aconductive graphite-doped pitch in a coating kettle. The coatingreaction is carried out in an argon atmosphere, the reaction temperatureis 750° C., and the reaction time is 12 hours. Finally, a silicon-basedanode material is obtained, which includes an inner core includingSiO_(x1) and the Si particle, and an outer shell layer of a carbon filmlayer doped with conductive graphite.

The secondary battery made with the foregoing silicon-based anodematerial has a reversible capacity of 1620 mAh/g, a first cycleCoulombic efficiency of 75%, and a 500-cycles capacity retention rate of32%.

TABLE 1 Examples, comparative examples and results Silicon 500- Massoxide raw cycles Content in Content in percentage material:carbon firstcycle capacity inner side outer side content source substance Temper-Incubation Reversible Coulombic retention of first of first M of the M(mass ature time capacity efficiency rate shell layer shell layerExample element (%) ratio) (° C.) (H) (mAh/g) (%) (%) (%) (%) Example1Li 10% 100:5 750 12 1430 89 88 4 45 Example2 Li  6% 100:5 750 12 1500 8582 2.5 36 Example3 Li  2% 100:5 750 12 1550 82 79 0.5 21 Example4 Li 10%100:5 850 12 1430 88 90 4.5 44.5 Example5 Li 10% 100:5 950 12 1400 90 865 43 Example6 Li 10% 100:5 750 8 1350 86 85 3 46 Example7 Li 10% 100:5750 16 1450 88 89 5 44 Example8 Na 10% 100:5 850 12 1200 78 83 2 46Example9 Mg 12% 100:5 950 12 1400 82 85 3 46 Example10 Al 11% 100:5 100012 1300 76 69 2.2 45 Example11 Fe 14% 100:5 950 12 1240 75 65 3 46Example12 Ca 10% 100:5 1000 12 1140 65 62 2 45 Comparative \ \ 100:5 75012 1650 76 30 \ \ example 1 Comparative \ \  100:10 750 12 1620 75 32 \\ example 2

As shown in Table 1, the secondary battery made of the secondary batteryanode material provided by the embodiments of the present applicationexhibits high delithiation capacity, high first cycle Coulombicefficiency and good cycle performance. In addition, the chargingcapacity is above 1400 mAh/g, the discharge capacity is above 1627mAh/g, and the first cycle Coulombic efficiency is above 86%.

Referring to FIG. 2, which is an SEM image of the silicon-based anodematerial provided in the embodiments of the present application, it canbe seen that the particles of the silicon-based anode material areevenly dispersed.

Referring to FIG. 3, which is the charge-discharge curve of thesilicon-based anode material provided in the embodiments of the presentapplication, it can be seen that the silicon-based anode material has ahigh reversible capacity and high first cycle Coulombic efficiency.

In summary, after reading the detailed disclosure provided above, aperson skilled in the art will understand that the disclosures aremerely some example, and do not limit the present application. Moreover,although not explicitly stated herein, a skilled in the art willunderstand that the present invention is intended to cover variouschanges, modifications and improvements of the embodiments. Thesechanges, modifications and improvements are intended to be proposed inthe present application and are within the spirit and scope of theexemplary embodiments of the present application.

It will be appreciated by a person of ordinary skill in the art that theterm “and/or” used herein includes any and all combinations of one ormore of the related items listed.

It will also be appreciated by a person of ordinary skill in the artthat the terms “comprise”, “comprising”, “include” and/or including,when used herein, refer to the presence of stated features, entities,steps, operations, elements and/or assemblies, but do not exclude thepresence or addition of one or more other features, entities, steps,operation elements, assemblies and/or combinations thereof.

It should also be understood that although the terms “first”, “second”,“third”, etc. may be used herein to describe various elements, theseelements may not be limited by these terms. These terms are merely usedto distinguish one element from another. Thus, a first element in someembodiments may be referred to as a second element in other embodimentswithout departing from the teachings of the present application.Moreover, the same reference symbols or reference numerals are usedthroughout entire disclosure to represent the same elements.

Furthermore, the exemplary embodiments are described by referring to thecross sectional and/or planar illustrations as the idealized exemplaryillustration.

1-20. (canceled)
 21. A silicon-based anode material for secondary batteries, comprising: an inner core, wherein the inner core includes an Si particle and silicon oxide SiOx₁, where 0<x₁<2; a first shell layer, wherein the first shell layer including a compound of the general formula M_(y)SiO_(z) and an elemental carbon, where 0<y≤4, 0<z≤5, and z≥x₁, and wherein M includes at least one of: Li, Na, Mg, Al, Fe, or Ca, the first shell layer covers the inner core, and the contents of M and the elemental carbon in the first shell layer gradually increase from one side of the first shell close to the inner core to another side of the first shell far away from the inner core; and a second shell layer, wherein the second shell layer includes a carbon film layer or a composite film layer formed of a carbon film layer and a conductive additive, and the second shell layer covers the first shell layer.
 22. The silicon-based anode material for secondary batteries according to claim 21, wherein the mass percentage content of M in the silicon-based anode material is 1-15%, and wherein the mass percentage of M is 1-40% of the first shell layer.
 23. The silicon-based anode material for secondary batteries according to claim 21, wherein the mass percentage content of M and the elemental carbon in the first shell layer increases in a gradient manner from a side of the first shell layer close to the inner core to a side of the first shell layer far away from the inner core.
 24. The silicon-based anode material for secondary batteries according to claim 23, wherein the mass percentage content of M on the side of the first shell layer close to the inner core is 0-5% of the first shell layer, and the mass percentage content of M on the side of the first shell layer far away from the inner core is 30-48% of the first shell layer.
 25. The silicon-based anode material for secondary batteries according to claim 21, wherein the elemental carbon includes at least one of: hard carbon, soft carbon, or amorphous carbon.
 26. The silicon-based anode material for secondary batteries according to claim 21, wherein the carbon film layer includes at least one of: hard carbon, soft carbon, or amorphous carbon, and the conductive additive includes at least one of carbon nanotube, graphene, conductive carbon black, vapor-grown carbon fiber, or conductive graphite.
 27. The silicon-based anode material for secondary batteries according to claim 21, wherein in the silicon-based anode material, the mass percentage content of the elemental carbon is 0.1-2%, the mass percentage content of the carbon film layer or the composite film layer formed by the carbon film layer and the conductive additive is 0.1-15%, and the mass percentage content of the conductive additive is 0-5%.
 28. The silicon-based anode material for secondary batteries according to claim 21, wherein a median diameter of the inner core is 1-10 μm, a thickness of the first shell layer is 0.01-2 μm, and a thickness of the second shell layer is 0.01-1 μm.
 29. The silicon-based anode material for secondary batteries according to claim 21, wherein the Si particles in the inner core are uniformly dispersed in the SiOx₁.
 30. The silicon-based anode material for secondary batteries according to claim 21, wherein based on the mass of the silicon-based anode material being 100%, a sum of the mass percentage contents of the Si particle, the silicon oxide SiOx₁ and the MySiO_(z) is 83-99%.
 31. A method for preparing a silicon-based anode material for secondary batteries, comprising: preparing a first mixture, wherein the first mixture includes a silicon oxide raw material SiO_(x), a metal source substance, and a carbon source substance, where 0<x<2; calcining the first mixture under a non-oxygen condition to obtain a first product, wherein the first product includes: an inner core, wherein the inner core includes an Si particle and silicon oxide SiOx₁, where 0<x₁<2, x₁>x; and a first shell layer, wherein the first shell layer covers the inner core, the first shell layer includes a compound of the general formula M_(y)SiO_(z) and elemental carbon, where 0<y≤4, 0<z≤5, and z≥x₁, and wherein M includes at least one of: Li, Na, Mg, Al, Fe, or Ca, the contents of M and the elemental carbon in the first shell layer gradually increase from one side of the first shell layer close to the inner core to another side of the first shell layer far away from the inner core; and passing the first product through the carbon source substance, or the carbon source substance and a conductive additive to perform a coating reaction, and then performing a carbonization treatment in a non-oxidizing atmosphere, such that a surface of the first shell layer is coated with a second shell layer, wherein the second shell layer includes a carbon film layer or a composite film layer formed by a carbon film layer and a conductive additive.
 32. The method for preparing a silicon-based anode material for secondary batteries according to claim 31, wherein the non-oxidizing atmosphere includes at least one of: nitrogen, argon, hydrogen, or helium.
 33. The method for preparing a silicon-based anode material for secondary batteries according to claim 31, wherein a mass ratio of the silicon oxide raw material SiO_(x) to a metal source substance ranges from 100:1 to 100:50, and a mass ratio of the silicon oxide raw material SiO_(x) to the carbon source substance ranges from 100:1 to 100:10.
 34. The method for preparing a silicon-based anode material for secondary batteries according to claim 31, wherein the metal source substance includes at least one of: a metal carbonate, a metal nitrate or a metal hydroxide, and the metal includes at least one of: Li, Na, Mg, Al, Fe, or Ca.
 35. The method for preparing a silicon-based anode material for secondary batteries according to claim 34, wherein the metal source substance includes at least one of: lithium citrate, lithium carbonate, lithium hydroxide, or lithium nitrate.
 36. The method for preparing a silicon-based anode material for secondary batteries according to claim 31, wherein the carbon source substance includes at least one of: citric acid, glucose, resin, coal pitch, petroleum pitch, polyvinyl alcohol, polyacrylonitrile, polymethyl methacrylate, sucrose, polyacrylic acid, or polyvinyl pyrrolidone.
 37. The method for preparing a silicon-based anode material for secondary batteries according to claim 31, wherein a temperature of the non-oxygen condition for calcining is 300-1000° C.; and a temperature of the carbonization treatment is 500-1200° C.
 38. The method for preparing a silicon-based anode material for secondary batteries according to claim 31, wherein the first mixture is a mixture of lithium citrate or lithium carbonate, citric acid and the silicon oxide raw material SiO_(x), where 0<x<2.
 39. The method for preparing a silicon-based anode material for secondary batteries according to claim 31, wherein the silicon oxide raw material SiO_(x) is a powder with a median particle size of 1-10 μm.
 40. A secondary battery, comprising: a silicon-based anode material including: an inner core, wherein the inner core includes an Si particle and silicon oxide SiOx₁, where 0<x₁<2, a first shell layer, wherein the first shell layer including a compound of the general formula M_(y)SiO_(z) and an elemental carbon, where 0<y≤4, 0<z≤5, and z≥x₁, and wherein M includes at least one of: Li, Na, Mg, Al, Fe, or Ca, the first shell layer covers the inner core, and the contents of M and the elemental carbon in the first shell layer gradually increase from one side of the first shell close to the inner core to another side of the first shell far away from the inner core, and a second shell layer, wherein the second shell layer includes a carbon film layer or a composite film layer formed of a carbon film layer and a conductive additive, and the second shell layer covers the first shell layer. 